1. Field of the Invention This invention relates to computer systems and, more particularly, to methods and apparatus for increasing the speed of operation of a central processing unit used in such systems.
2. History of the Prior Art
Computers are capable of doing more work if they can process information faster. One way in which this may be accomplished is to run the central processing unit faster. As long as the circuitry can operate at a faster speed and the processes are capable of running at that speed, such an operation will produce more work.
A problem with running a central processing unit at a faster speed is that many of the components which function with the processor are not designed to run at such a speed. To redesign those components to run faster would be very expensive, time consuming, and would produce expensive components. Even though accomplished, it would be impossible to run such central processors with older components external to the processor. Consequently, it is desirable to run a central processing unit at a faster clock frequency than the clock frequency at which components of the computer external to that central processor are run. Running the central processing unit at a faster clock frequency may be accomplished by providing clock generating circuitry within the central processing unit which runs at a faster rate than does a system clock generating circuit. However, in order to run with such external components, the central processing unit must interface with the external components at a slower speed. It has been found possible to operate a central processor internally at a speed which is twice the speed at which external circuitry is designed to operate, yet allow the processor to interface at a slower rate for operations which involve external circuitry, and still increase the overall speed of operation of a computer significantly. This increase of overall speed occurs because a substantial amount of the actual processing may be accomplished by the processor without requiring it to receive or send data to external components. The i486 DX2 processors designed and manufactured by Intel Corporation of Santa Clara, Calif., accomplish this feat.
The success of computers utilizing these processors has suggested that further increases in the operational speed would be beneficial. However, since computer systems now exist which utilize central processors which function at an internal speed which is twice the speed of external components and other processors which function at the speed of external components, it is desirable that any circuitry used for interfacing and synchronizing be capable of interfacing and synchronizing any central processor running at the external clock rate, running at twice the external rate, and running at an even more rapid internal clock rate. Circuitry which allows this will greatly reduce the overall cost of the systems using different processors operating at the different clock speeds. This desirable feature creates an even greater interfacing problem.